The present invention relates to a device for solid phase microextraction and analysis, particular to a sheath which resolves problems associated with the fragile fiber coated with the active extraction media for solid phase microextraction devices, and more particularly to a porous protective sheath which contains the active extraction media used in solid phase microextraction.
Solid phase micro-extraction (SPME) is a chemical sampling technique which adsorbs/absorbs the analyte from the sample without the use of solvents or the need for exhaustive extractions. The active portion of the SPME device usually consists of a small diameter (50-300 μm) fused silica fiber coated with 10-200 μm of an active absorbent or media. The absorbing material can be a wide variety of organic or inorganic materials. Some examples of commercially available media include polydimethyl siloxane, bonded divinylbenzene/styrene spheres, activated carbon spheres, etc. The coated fiber is housed in the needle of a GC-MS syringe, and can be mechanically extended and thus exposed to both collect analytes from the environment or sample fluid and desorb analytes into the GC injection pod. The fiber is retracted into the needle when not in use.
In the past, the SPME technique has several major drawbacks including: fiber breakage due to mechanical stress, unintentional physical contact, and or vibration; 2) gross media coating loss from the fiber due to accidental physical contact of the exposed coated fiber; and minor coating loss due to general decohesion of the bonded particulate coatings when exposed to the environment.
FIG. 1 illustrates the SPME process and shows the operation of a typical fiber/syringe assembly, such as exemplified by U.S. Pat. No. 5,691,206 issued Nov. 25, 1997 to J. B. Pawlisyn. The coated SPME fiber (hereafter referred to as fiber) is stored fully retracted inside the syringe needle. To clean (activate), expose, and desorb the fiber, the plunger is depressed and the fiber is extended out of the needle. After exposure, the plunger is released and a spring-operated mechanism retracts the fiber into the needle to protect it. The fiber remains in the needle during the septum piercing operation when the sample is injected into the GC or HPLC port. The fiber is then extended into the inlet port to desorb the sample into the GC or HPLC.
It is apparent that the exposure of the extended, unprotected fiber causes a high risk of mechanical breakage of the fiber or coated media loss, particularly when the fiber is used for general environmental air or H2O sampling such as a smokestack, lake, waste oil, etc., which is not done under laboratory conditions. In addition, the sliding action of the fiber in the needle as well as its unprotected exposure to the environment can easily cause a gross or minor amount of coating loss. Both fiber breakage and loss of coating can often go unnoticed, which will cause either a change in performance of the fiber or complete failure of the fiber. The user can thus unknowingly collect erroneous data.
The present invention minimizes the above-referenced problems by the use of a porous protective sheath which prevents fiber breakage and minimizes media loss. The porous protective sheath contains the active extraction medium therein and replaces the coated fiber. Use of this sheath eliminates the need for complete unprotected exposure of the fiber. Basically, porosity of the sheath is provided a number of openings or slots via which the active media contained within the sheath is exposed to the selected environment, sample, etc. The sheath is of sufficient strength for the septum piercing operation, and may have an open or pointed end. The porous sheath may be mounted so as to retract into the needle of the device of above referenced U.S. Pat. No. 5,691,206 in place of the fiber, or replace the needle and the fiber of that device, but would be subjected to exposure of the environment unless the pores, openings or slots thereof were covered.